LeetCode – Super Ugly Number (Java)

Write a program to find the nth super ugly number.

Super ugly numbers are positive numbers whose all prime factors are in the given prime list primes of size k. For example, [1, 2, 4, 7, 8, 13, 14, 16, 19, 26, 28, 32] is the sequence of the first 12 super ugly numbers given primes = [2, 7, 13, 19] of size 4.

Note:
(1) 1 is a super ugly number for any given primes.
(2) The given numbers in primes are in ascending order.
(3) 0 < k < = 100, 0 < n < = 106, 0 < primes[i] < 1000.

Java Solution

Keep adding minimum values to results and updating the time value for the chosen prime number in each loop.

public int nthSuperUglyNumber(int n, int[] primes) {
    int[] times = new int[primes.length];
    int[] result = new int[n];
    result[0] = 1; // first is 1
 
    for (int i = 1; i < n; i++) {
        int min = Integer.MAX_VALUE;
        for (int j = 0; j < primes.length; j++) {
            min = Math.min(min, primes[j] * result[times[j]]);
        }
 
        result[i] = min;
 
        for (int j = 0; j < times.length; j++) {
            if (result[times[j]] * primes[j] == min) {
                times[j]++;
            }
        }
    }
 
    return result[n - 1];
}